@Esther_Bunbury copy and paste mostly does that, it even creates unnecessary spaces where there were no spaces from where you copied it. After pasting your text, try to preview, it will correct the errors, and you can even go back to rich text to make some adjustments your self, this is how I correct this error my self. I have seen it before when I was using copy and paste from a word document. I hope this will hep you.
You can use every editor to write your post, What is important is that, when you paste your post on Connect, you should remember to “paste as plain text”.
Every editor add in fact extra, hidden characters, that are needed for formatting the text (font, size, colour, etc). All this is using unnecessary space, and can also cause some HTML error.
When you “paste as plain text”, all the extra information will be removed. Then, you can format your text directly here, if needed, adding bold and italic.